Method for producing phosphonium phenolates

ABSTRACT

The invention relates to a method for producing phosphonium phenolates from phosphonium halogenides and phenols.

[0001] This application relates to a process for the production ofphosphonium phenolates.

[0002] The production of phosphonium phenolates has already beendescribed in DE-A-197 273 51. However, the phosphonium phenolatesproduced in this manner contain impurities which are disadvantageous forsubsequent use. It is thus known that phosphonium phenolates may be usedas transesterification catalysts for melt transesterification. Purityis, however, of vital significance for this application as impuritiesmay result in discolouration, variations in activity or secondaryreactions in the transesterification process. Moreover, this processgenerates a considerable quantity of solvent as waste product, whichentails elevated disposal costs. The product is furthermore exposed toelevated temperatures during removal of residual solvent. Sincephosphonium phenolates readily form addition products with phenol,exposure to elevated temperatures should be kept as slight as possible.

[0003] The object of the present application is accordingly to provide aprocess in which exposure to elevated temperatures and the quantity ofsolvent generated remain as slight as possible, but in which the purityof the phosphonium phenolate is as high as possible.

[0004] The application provides a process for the production ofphosphonium phenolates by reacting phosphonium halides and phenols in anaqueous alkaline solution, which is characterised in that thephosphonium phenolate produced is separated from the synthesis mixtureby crystallisation.

[0005] The reaction is preferably performed at temperatures of 0 to 55°C., in particular of 15 to 50° C.

[0006] The reaction is preferably performed at molar ratios of phenol tophosphonium halide of 2:1 to 10:1, preferably of 4.5:1 to 6:1 and inparticular of 5:1.

[0007] The reaction is preferably performed at pH values of 9.5 to 11,preferably of 9.5 to 10.5 and in particular of 10 to 10.5.

[0008] The reaction is optionally performed in the presence of alcoholsin quantities of 50 wt. % to 200 wt. %, preferably of 66 wt. % to 125wt. %, relative to the quantity by weight of the aqueous phase, whereinthe alcohols preferably have a solubility in pure water of at most 15wt. %.

[0009] The phosphonium phenolates produced in this manner contain nomore than 0.1 wt. % of halide.

[0010] Phosphonium halides of the formula (I) are in particular used forthe reaction

[0011] in which

[0012] R₁ to R₄ identical or different, each denote a C₁-C₁₂ alkyl,C₅-C₆ cycloalkyl, C₇-C₁₂ aralkyl or C₆-C₁₄ aryl residue and

[0013] X⁽⁻⁾ denotes a halide ion, preferably F⁽⁻⁾, Cl⁽⁻⁾ or Br⁽⁻⁾ and

[0014] n denotes the number 1 or 2, wherein, when n=2, R₄ denotes aC₂-C₁₂ alkylene residue.

[0015] Residues R₁ to R₄ are preferably identical or different and eachdenote a C₆-C₁₄ aryl residue or the residues R₁ to R₃ each denote aC₆-C₁₄ aryl residue and R₄ denotes a C₂-C₁₂ alkylene residue.

[0016] Such phosphonium halides and the production thereof are known orare obtainable using known methods (c.f. for example Houben-Weyl,Methoden der organischen Chemie, volume XII/1, pages 79 et seq. andWorrall, J. Amer. Chem. Soc. 52 (1930), pages 293 et seq.).

[0017] These compounds (I) are formed on the reaction of trialkyl- ortriarylphosphines, for example of triphenylphosphine, with haloaryleneor haloalkylene, for example benzyl bromide, in the presence of metalsalts (Friedel-Crafts alkylation) or in the presence of Grignardcompounds and cobalt(II) chloride.

[0018] Phenols which are preferred for the reaction are phenol orsubstituted phenols as well as bisphenols.

[0019] Particularly preferred phenols are those of the formula (II)

[0020] in which

[0021] R₅ to R₇ mutually independently denote H, C₁-C₁₂ alkyl, C₅-C₆cycloalkyl, C₇-C₁₂ arylalkyl and C₆-C₁₄ aryl; R₅ to R₇ preferably denotehydrogen.

[0022] Such phenols are known from the literature.

[0023] Phosphonium phenolates of the formula (III) are preferablyproduced

[0024] in which the residues R₁ to R₇ and n have the above-statedmeanings.

[0025] Completely deionised water or distilled water is preferably usedto produce the aqueous alkaline phase.

[0026] The pH value of 9.5 to 11.0, preferably of 9.5 to 10.5,particularly preferably of 10.0 to 10.5 is preferably established usingan alkali metal hydroxide solution, preferably sodium hydroxide solutionor potassium hydroxide solution, while taking the buffering action ofphenol/Na phenolate into account.

[0027] The process according to the invention may be performedcontinuously or discontinuously, wherein discontinuous operation ispreferred.

[0028] According to a preferred method, phenol, phosphonium halide andalcohol are initially introduced as a solution and water is added. ThepH value is adjusted, optionally with cooling, to values 9.5 to 11.0,preferably of 9.5 to 10.5, particularly preferably of 10.0 to 10.5 byaddition of alkali metal hydroxide solution. The temperature of 0 to 55°C., preferably of 15 to 50° C. is maintained during this operation,preferably by vigorous stirring of the reaction components. The durationof the reaction should be less than 2 hours, preferably less than 1hour.

[0029] The phosphonium phenolate produced according to the invention isisolated, preferably by separating the aqueous phase from the organicphase using an alcohol which is sparingly soluble in water (thesolubility of alcohols in water is known from the literature) andextracting the organic phase at least once, preferably three times withcompletely deionised water or distilled water. The solution is thencooled to 26 to 0° C., preferably to 23 to 10° C. The precipitatedphenolate is then separated by suction filtration and purified bywashing. The resultant product is optionally recrystallised and dried.

[0030] Alcohols suitable according to the invention for the reactionsolution are aliphatic alcohols of the formula C_(n)H₂₊₁—OH, in which nis an integer from 4 to 10 inclusive, such as for example n-butanol,isobutanol, n-pentanol, methylbutanols, neopentanol, amyl alcohols,branched and unbranched hexanols, heptanols, octanols, nonanols ordecanols.

[0031] Alcohols suitable according to the invention for the reactionsolution are also cycloaliphatic alcohols of the formulaC_(n)H_(2n−1)—OH, in which n is an integer from 5 to inclusive, such asfor example cyclopentanol, methylcyclopentanols, cyclopentanemethanol,cyclopentylpropanols, cyclohexanol, cyclohexylethanols,cyclohexylpropanols, cyclohexylbutanols, methyl-, ethyl-, propyl- andbutylhexanols, cycloheptanols, cyclooctanols.

[0032] Apart from completely deionised water, alcohols may also be usedfor washing the phenolate. In this case, apart from those for thereaction solution, water-soluble alcohols may also be used, such as forexample ethanol, n-propanol or isopropanol.

[0033] Propanols, in particular isopropanol, are preferred in this case.Polyhydric aliphatic or cycloaliphatic alcohols may also be usedaccording to the invention.

[0034] Preferred aliphatic alcohols are propanols, (iso)butanols,pentanols and hexanols, in particular isobutanol and isopropanol.

[0035] Preferred cycloaliphatic alcohols are cyclopentanol,cycloheptanol and cyclooctanol, particularly preferably cyclohexanol.

[0036] The weight ratio of water to alcohol is between 2:1 and 1:2,preferably between 1:1 and 1:2.

[0037] The alcohols to be used according to the invention are added toimprove working up, as the phenol/alcohol mixture has a lower densitythan the aqueous solution and the organic phase is thus above theaqueous phase. The aqueous phase may thus be drained off from beneath,the organic phase, which contains the phenolate, may be washed withcompletely deionised water in the same separating vessel and the washingwater again drained off from beneath.

[0038] If the alcohol is not added, only the aqueous saline solution isheavier than the organic phase and may be drained off from beneath.Phase inversion occurs on further washing with completely deionisedwater, the organic phase is heavier and thus beneath the aqueous phase.This working up method is more elaborate because a second working upvessel is required.

[0039] Quaternary phosphonium phenolates produced according to theinvention are in particular compounds of the formulae

[0040] Using the process according to the invention, it is possible toproduce phosphonium phenolates in elevated yields and at high purity.

[0041] The phosphonium phenolates produced in this manner are suitablein particular as catalysts for esterification and transesterification,in particular for the production of polycarbonates by the melttransesterification process (c.f. U.S. Pat. No. 3,442,854).

[0042] As is known, the melt transesterification process starts, forexample, from aromatic diphenols, carbonic acid diaryl esters andoptionally branching agents and/or monophenols.

[0043] The phosphonium phenolates obtainable according to the inventionare used as catalysts in this case in quantities of 10⁻¹ mol to 10⁻⁸mol, preferably in quantities of 10⁻³ mol to 10⁻⁷ mol, per mol ofdiphenol.

[0044] Further details of the melt transesterification process aredescribed in the literature (c.f. Hermann Schnell, Chemistry and Physicsof Polycarbonates, Polymer Reviews, volume 9, 1964, pages 44 to 51,DE-A-1 031 512, U.S. Pat. Nos. 3,022,272, 5,340,905 and 5,399,659).

[0045] The thermoplastic polycarbonates produced with the phosphoniumphenolates obtainable according to the invention are solvent-free, havea light inherent colour and are largely free of unwanted defects in thepolycarbonate.

[0046] The polycarbonates produced in this manner may be usedindustrially in the form of the most varied mouldings in anyapplications in which thermoplastic polycarbonates have hitherto beenused, such as in electrical engineering, as lamp covers, as safetyscreens or as optical data storage media, such as CD material.

EXAMPLES Comparative Example 1

[0047] 376 g (4.0 mol) of phenol, 800 ml of completely deioinsed water,335.44 g (0.8 mol) of tetraphenylphosphonium bromide and 640 g ofisobutanol are initially introduced into a 2 L round-bottomed flaskequipped with a stirrer, thermometer and dropping funnel and are stirredat 20° C. to 25° C. 79 g (0.97 mol) of 49% sodium hydroxide solution areadded dropwise within approx. 5 minutes, the pH value is checked with aglass electrode—it must be within a range from 9.5 to 11.0. The mixtureis then stirred for 0.5 h at 45° C. After phase separation, the loweraqueous phase is drained off and the organic phase is washed three timeswith completely deionised water, it being possible in each case to drainoff the washing water, as the heavier phase, from beneath. Theisobutanol is then removed by distillation under a water-jet vacuum at50° C.

[0048] The crystalline residue is dried under a vacuum at 100° C. Theyield, determined using the P-NMR method, is 98.2% of the theoreticalyield.

[0049] The results are shown in Table 1.

Example 1

[0050] 376 g (4.0 mol) of phenol, 800 ml of completely deionised water,335.44 g (0.8 mol) of tetraphenylphosphonium bromide and 640 g ofisobutanol are initially introduced into a 2 L round-bottomed flaskequipped with a stirrer, thermometer and dropping funnel and are stirredat 20° C. to 25° C. 79 g (0.97 mol) of 49% sodium hydroxide solution areadded dropwise within approx. 5 minutes—the pH value is adjusted to arange from 9.5 to 11.0. The mixture is then stirred for 0.5 h at 45° C.After phase separation, the lower aqueous phase is drained off and theorganic phase is washed three times with completely deionised water, thewashing water, as the heavier phase, in each case being drained off frombeneath. The organic phase is then cooled to room temperature whilebeing stirred, the product crystallising out during this operation.After at least 4 hours' crystallisation time, the product is removed byvacuum filtration. After NMR analysis for the content of phenol,isobutanol and tetraphenylphosphonium phenolate, the filtrate isreturned to the reaction. The crystalline residue is rewashed with2-propanol and then dried under a water-jet vacuum at 100° C.

[0051] The results are shown in Table 1. TABLE 1 Comparative Example 1Example 1 Na [ppm] 0.7 <0.5 Br [ppm] 0.7 0.01 Colour light greycolourless

Examples of Use

[0052] B1) 114.15 g (0.500 mol) of bisphenol A and 113.54 (0.530 mol) ofdiphenyl carbonate are weighed out into a 500 ml three-necked flaskequipped with a stirrer, internal thermometer and Vigreux column (30 cm,mirrored) with bridge. Atmospheric oxygen is removed from the apparatusby applying a vacuum and flushing with nitrogen (3 times) and themixture heated to 150° C. 0.0173 g (4×10⁻³ mol %) oftetraphenylphosphonium phenolate (TPP-P) produced according to Example1, relative to bisphenol A, are then added as a 3% phenolic solution andthe resultant phenol removed by distillation at 100 mbar. Thetemperature is simultaneously raised to up to 250° C. The vacuum is thenimproved stepwise to 1 mbar and the temperature raised to 260° C. Thetemperature is then raised to 280° C. and the mixture stirred for 1.5hours at 0.1 mbar. A light-coloured, solvent-free polycarbonate isobtained having a relative solution viscosity of 1.250 (dichloromethane,25° C., 5 g/l).

[0053] The content of branching agent of the formula (VII) in theresultant polycarbonate is 25 ppm. The phenolic OH value of thepolycarbonate is 70 ppm.

[0054] B2) As Example B1), except that the temperature is raised from260° C. to 300° C. and the mixture is stirred for 1.5 hours at 0.1 mbar.A light-coloured, solvent-free polycarbonate having a relative solutionviscosity of 1.300 (dichloromethane, 25° C., 5 g/l) is obtained. Thecontent of branching agent of the formula (VII) in the resultantpolycarbonate is 18 ppm. The phenolic OH value of the polycarbonate is55 ppm.

1. Process for the production of phosphonium phenolates by reactingphosphonium halides and phenols in an aqueous alkaline solution,characterised in that the phosphonium phenolate produced is separatedfrom the synthesis mixture by crystallisation.
 2. Process according toclaim 1, characterised in that the reaction is performed at temperaturesof 0 to 55° C.
 3. Process according to at least one of claims 1 or 2,characterised in that the reaction is performed at molar ratios ofphenol to phosphonium halide of 2:1 to 10:1.
 4. Process according to atleast one of claims 1 to 3, characterised in that the reaction isperformed at pH values of 9.5 to
 11. 5. Process according to at leastone of claims 1 to 4, characterised in that the reaction is performed inthe presence of alcohols in quantities of 66 wt. % to 125 wt. %. 6.Process according to at least one of claims 1 to 5, characterised inthat crystallisation proceeds from an alcoholic solution.
 7. Processaccording to claim 6, characterised in that the alcohol used isisobutanol.
 8. Process according to at least one of claims 1 to 7,characterised in that the organic phase used is continuouslyrecirculated.
 9. Phosphonium phenolates obtainable according to aprocess as defined in any of claims 1 to
 8. 10. Phosphonium phenolateshaving a halide content of no more than 0.1 wt. %.
 11. Use of thephosphonium phenolates defined in claim 9 as a catalyst fortransesterification reactions.
 12. Use of the phosphonium phenolatesdefined in claim 9 as a transesterification catalyst for the productionof polycarbonate.